半干旱区油松林分夜间液流变化特征及其影响因子

Nocturnal sap flow variations and its influencing factors of Pinus tabulaeformis stand in a semi-arid environment

近年来,随着大气温度升高,树木蒸腾加剧,森林经营管理面临水资源短缺等一系列问题。夜间液流作为树干液流的重要组成部分,对准确估算林分耗水及水资源管理有着重要意义。于2019年生长季,以呼和浩特市树木园60年生油松为研究对象,采用热扩散法(TDP探针)测定树干液流,同步监测林外环境因子,以揭示半干旱区油松夜间液流调控机制。结果表明:1)生长季油松林分夜间液流呈现出明显的日、月变化。在日尺度上,油松林分夜间液流速率呈单一递减趋势,各月在00:00前均可以观测到明显夜间液流,且00:00前液流速率下降幅度更为明显;在月尺度上,油松林分夜间液流量5月最大,其次依次为9月>6月>8月>7月。2)在日尺度上,生长季油松林分夜间液流量与饱和水汽压差、土壤相对含水量和日间液流量呈显著正相关(P<0.05),与风速呈显著负相关(P>0.05)。生长季油松林分夜间液流平均贡献率为7%,不同影响因子对夜间液流贡献率的作用大小依次为日间液流量>饱和水汽压差>日间太阳总辐射。研究发现:生长季油松林分各月均存在明显的夜间液流,环境因子与油松林分夜间液流存在显著相关(P<0.05)。在林分尺度计算生长季各月液流量时,若不考虑夜间液流,月液流量将被低估3.0%~11.5%。

[Background]In recent years,the increase of atmospheric temperature has led to the aggravation of tree transpiration,and the management of forest land faced a series of problems such as water shortage.As an important part of sap flow,nocturnal sap flow is of great significance for accurate estimation of water consumption and water resource management of forest.[Methods]In the growing season of 2019,selecting Pinus tabulaeformis in the arboretum of Hohhot as the research object,the thermal diffusion method(TDP thermal probe)was used to measure sap flow,precipitation(mm),air temperature(℃),relatively humidity(%),wind speed(m/s),and global radiation(W/m2)were measured continuously with an Dynamet automatic weather station(Dynamet,USA).Soil water content was measured half-hourly at depths of 10 to 50 cm in each plot using the 5TE soil water sensor(Decagon,USA).All statistical analyses were carried out with SPSS 24.0 and Excel 2013,and significance was reported at the 0.05 level.[Results]1)The nocturnal sap flow of P.tabulaeformis stand showed obvious daily and monthly variations in growing season.On the daily scale,nocturnal sap flow velocity of P.tabulaeformis stand showed a single decreasing trend.Nocturnal sap flow can be observed before 0 o'clock in each month and the decreased range of nocturnal sap flow velocity before 0 o′clock was more obvious.On the monthly scale,the stand nocturnal sap flow of P.tabulaeformis stand was the largest in May,followed by September>June>August>July.2)On the daily scale,the nocturnal sap flow of P.tabulaeformis stand showed significant positive correlation with vapor pressure deficit,diurnal sap flow and relative extractable water(P<0.05),and showed significant negative correlation with wind speed(P<0.05)in growing season.The average contribution of nocturnal sap flow of P.tabulaeformis stand in growing season was 7%,the effect of different influencing factors on ratio of nocturnal sap flow to total sap flow was in the order of diurnal sap flow>vapor pressure deficit>global radiation.[Conclusions]There is a significant nocturnal sap flow of P.tabulaeformis stand in growing season,and environmental factors were significantly correlated with the nocturnal sap flow(P<0.05),if the nocturnal sap flow was not taken into account at stand scale in growing season,the monthly sap flow will be underestimated by 3.0%-11.5%.